1. Field of the Invention
The invention is an improved process for preparing overbased sulfonates which are used as detergent and reserve alkalinity lubricating oil additives.
2. Description of Other Related Methods in the Field
In the course of operation, internal combustion engines convert lubricating oil to acidic degradation products. Those acidic degradation products attack and corrode engine parts and catalyze the formation of sludge, thereby reducing lubricity and accelerating wear of moving parts in contact with the lubricating oil.
It is desirable to add substances to the lubricating oil which neutralize acids as they are formed in the engine before they reach concentrations sufficient to cause corrosion or to catalyze the sludge reaction. Adding alkalinity agents to the detergent in motor oil for this purpose is known as overbasing. Colloidal carbonates of alkaline earth metals have been found to be well suited for this purpose. These colloidal carbonate dispersions are stabilized by oil soluble surface active agents such as sulfonates of the alkaline earth metals in which the sulfonic acid portion of the molecule has a molecular weight of preferably 450 to 600. The sulfonates are made by sulfonation of lubricating oil fractions from petroleum and by sulfonation of alkyl benzenes having the required molecular weight. Benzene alkylates with straight chain alkyl groups are especially effective.
U.S. Pat. No. 4,780,224 to Tze-Chi Jao teaches a method of preparing overbased calcium sulfonates. In the method, calcium hydroxide is formed in situ by first adding 25% of the total water and then adding the remainder of the water to calcium oxide during hydration and carbonation.
U.S. Pat. No. 4,810,396 to Tze-Chi Jao et al. teaches a process for preparing overbased calcium sulfonates. In the method the entire amount of calcium oxide, calcium hydroxide and water are charged in a specified ratio before carbonation.
U.S. Pat. No. 4,604,219 to J. R. Whittle teaches a method of preparing overbased calcium sulfonates. In the method calcium hydroxide is formed in situ by the continuous and uniform addition of water to calcium oxide over the entire hydration and carbonation time rather than incrementally. Water rate and amount were found to be critical.